Is a Vacuum Bed Necessary?

      CNC owners discuss the types of work that benefit from vacuum-table equipment, and describe other methods for holding parts down. November 8, 2007

I'm going to use a CNC to router cut some picture frame and clock templates from a sheet of MDF (1200 x 1000 x 15 mm). (The smaller clock templates are placed inside the frame templates to make best use of the material.) I'm wondering if, to get clean and accurate cuts without having problems with the material moving, I will need to use a vacuum bed? In the picture below, the MDF sheet is shown in yellow and shapes to be cut out are in orange. I'm hoping I will be able to do this type of work without having to buy a vacuum bed for the CNC router.

Forum Responses
(CNC Forum)
From contributor V:
You can leave 1-2mm of material and then remove the parts with a hand-held router fitted with a ball-bearing bit. What kind of hold-down system are you currently using?

From the original questioner:
I'm currently looking to buy a CNC router and I just need an idea as to whether I should also get a vacuum bed. When you say I should maybe leave 1-2mm, are you talking about the thickness on the MDF, routing down 13-14mm, or are you talking about routing completely through the sheet, but leaving small 1-2 mm tags on each of the items to be cut out?

From contributor Z:
If you don't get a vacuum pump with a router, you will be sorry you didn't. You will constantly have to figure out clever methods of securing parts when you could be just pressing an on/off button to a vacuum pump. Just think about your MDF project that has to have the "rough" surface you mentioned in a previous post. Without vacuum or double stick tape, the MDF will not be perfectly flat on the table when you fly cut it, resulting in thick and thin spots in random places on the sheet. MDF or plywood does not have enough flexibility to use its own weight to lay perfectly flat on a machine table. Adding a mid range vacuum pump to a machine should cost about $5-7k.

From contributor S:
I have been using my CNC without a vacuum table for about ten years now. After hearing all the issues others have been having when changing materials, etc., I like it the way it is. We pin nail the parts to the spoil board, which does not take very long. When finished, pull the parts off, snap the nails off, and leave part of the nail in the MDF. Only problem we run into is when operator forgets to load the nail gun. It even works on small parts. When programming, we write it so that the first pass shows you where the parts will be, you nail it down and continue. We change the spoilboard about once a month.

From contributor Z:
Using a pin nailer is a great way to hold parts down, but it doesn't work on all materials. I too have used a pin nailer with plastic nails for certain applications and it has worked great, but it does not allow you the flexibility that vacuum pump does. The cool thing about the CNC world is that there are many ways to skin the cat and all I am saying is that a vacuum pump will only add to your choices of skinning that cat.

From contributor S:
Good point. We only cut MDF and HDPE, so we either nail or screw it in place.

From contributor W:
I've cut thousands of parts with no vacuum table on an AXYZ machine and never had a problem cutting things like the picture above. We would clamp the edges and leave a small tab on the part that we would sand off after. We would cut right through and make sure that we cut out the shapes in a logical order so the sheet was always the strongest until it had to be cut.

From contributor M:
I agree with contributor Z. If you are going to invest, get it. I didn't have the 5k extra, but we leave .005 or so and then sand the back and it pops out. You only need to leave enough not to get the part sucked up by the vacuum system.

From contributor T:
One idea here would be to get a vacuum system with a gasketed spoil board under the material to be cut, especially if this will be a repetitive cutting process. The gasket is offset slightly to the interior of the cuts and the inside is machined out for the vacuum to pull through. It requires a one time template to be made up and will work very well after that.

From contributor S:
What contributor T is saying is the very reason I am glad I don't have a vacuum table. We have hundreds of parts and products we cut on a regular basis. If we had to have a gasketed spoil board for each one of them, I would have to add on to my shop just to store them. I do agree that a vacuum table has its advantages. You have to see one in operation and see if it applies to what you are doing with it. We might cut two tabletops, then switch to computer desks, then to shelving all in an hour's time. I consider it an advantage to not have to change spoil boards each time as well.

From contributor W:
Contributor S, I totally agree. When I worked at a sign shop, almost every sign was different, and the letters I cut were always different, so no vacuum was an advantage to me since everyday was something new. If you're creating thousands of the same parts, then yes, vacuum is the way to go.

From contributor R:
No one seems to be mentioning a matrix table with a spoilboard. I have cut thousands of parts, even small ones, with this setup. If I am really concerned about the parts, I will leave tags (or an "onion skin"). Leave just a thin layer on the first major pass, then clean it up with a second pass. I agree that dedicated gasketed spoilboards can be a pain. However, if the questioner is going to run this batch on a regular basis, that's not a bad idea. I'm really surprised to see so many people not using a vacuum system. Interesting.

From contributor L:
We nest cut on a Komo 5x10 and every sheet is different. On very small parts we will either onion skin or tab, but most of the time it's just the vacuum (40hp Quincy screw). Cycle time is 7 minutes per 5x10x3/4 sheet. There is no damage from pins, no time wasted clamping. About once a day the MDF spoil board sheet is faced using a 4" diameter inserted bit. Only a few .001's are taken off each time and it takes less than 5 minutes to resurface the board. Time is money!

From the original questioner:
Does anyone know if using a mill-through mat might be a good idea? I'm not sure actually how this item works, but I assume you place the mat on top of the vacuum bed and then place the sheet of MDF on the very top. Would this mean I would not need to use any spoilboards?

From contributor K:
Contributor L, was wondering when you have a new sheet on your machine covering the entire 5 x 10 available area, how many in/hg does your 40 hp Quincy pull before you start cutting through the material?

From contributor L:
I just went out and watched it. The 1/2" MDF spoil board had been re-surfaced first thing this morning, so it was in pretty good shape. The router started cutting nested parts at 6:10am. It was cutting a 5x10x3/4" particleboard nest when I went out to watch and reply to your question (3 pm). At the start, before cutting, it read 27" on the gage. At the finish of cutting the nest, it was reading 24.5". There were a lot of relatively small parts, so it had been set to onion skin the parts, meaning that it had cleared the 3/8" kerf instead of packing it as it would normally do with a through cut (3/8" compression spiral bit being used). So it was bleeding more air than it would normally do. The fact that it was cutting particleboard rather than melamine or laminated board also meant that it was losing a little more vacuum too.

We have about 90' of 4" PVC pipe and seven 90ís between the pump and the router so we can locate the pump outside in a shed. There is also about 6í and two 90ís after the separator on the Quincy pump to let it blow the hot air outside of the shed. That way we don't have to listen to it or have all the heat in the shop in the summer. In the winter we pull the heat back into the shop through an insulated duct using a 1/2hp fan. That same fan circulates shop air back to the shed to keep the pump sort of warm so it doesnít have to start really cold in the winter mornings. It may not be the greatest piece of engineering, but it works. Next I need to do something similar for the compressed air system. We have the 25hp screw in a small room to control noise. We pull lots of air through that room using the fans on an air-to-air cooler, then the air goes to a refrigerated drier. Always something to be worked on.

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